The present invention relates to a developer which is suitable for developing negative-working exposed reproduction layers which may also contain an organic binder.
Light-sensitive reproduction layers are used, for example, in the preparation of offset printing forms or of photoresists (below, both these are called copying materials), that is to say they are in general applied by the user or the industrial manufacturer to a support. The supports used in these copying materials are metals, such as zinc, magnesium, chromium, copper, brass, steel, silicon, aluminum or combinations of these metals, plastic films, paper or similar materials. These supports can be coated with the light-sensitive reproduction layer without any modifying pretreatment, but preferably they are coated after carrying out a surface modification, such as mechanical, chemical and/or electrochemical roughening, an oxidation and/or a treatment with agents rendering the surface hydrophilic (for example, in the case of supports for offset printing plates). In addition to at least one light-sensitive compound, the conventional reproduction layers contain in most cases also an organic binder (resins or the like) and, optionally, also plasticizers, pigments, dyes, wetting agents, sensitizers, adhesion-promoters, indicators and other customary auxiliaries. After they have been exposed, the reproduction layers are developed in order to produce an image from them. For example, a printing form or a photoresist is obtained in this way.
A developer for negative-working reproduction layers must be capable of dissolving those parts of the layer (the later non-image areas) which have not been struck by electromagnetic radiation (e.g., light) away from the exposed layer without substantially affecting those parts of the layer (the later image areas) which have been struck by the radiation. In German Offenlegungsschrift No. 2,065,732 (=U.S. Pat. No. 3,867,147) which can be mentioned as a representative example, the following are listed as examples of suitable developers: water, water/organic solvent mixtures, aqueous salt solutions, aqueous acid solutions, aqueous-alkaline solutions and undiluted organic solvents, to which, if appropriate, surfactants and/or agents for rendering the surface hydrophilic can be added. The developers primarily used in the examples of this publication contain water, sodium lauryl-sulfate, sodium sulfate, tartaric acid and in some cases benzyl alcohol. Other developers contain, or are composed of, isopropanol, n-propanol, n-propyl acetate, polyacrylic acid, 1,1,1-trichloroethane, acetone or ethylene glycol monomethyl ether. As a rule, the most effective developers for such negative-working reproduction layers, however, have hitherto contained surfactants, so that foaming of the developer occurs, in particular in the case of developing in a machine.
In addition to the developer components already mentioned, the following have also been disclosed in the state of the art:
In German Auslegeschrift No. 1,193,366 (=U.S. Pat. No. 3,201,241), an aqueous developer for positive-working reproduction layers is described, which also contains complex formers and/or hydrophilic polymers in addition to a component having an alkaline reaction and a cation such as Be.sup.2+, Hg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Bi.sup.3+ or La.sup.3+ (the anions mentioned also include, inter alia, those of aliphatic carboxylic acids). In a relatively large list of compounds, salicylic acid (2-hydroxybenzoic acid) is also mentioned as a complex former. The developers should have pH values from 10.5 to 12.2, preferably from 10.9 to 11.5. The complex formers should be present in the developer in a quantity from 0.001 to 0.25% by weight, preferably from 0.07 to 0.1% by weight.
From German Offenlegungsschrift No. 2,353,992 (=U.S. Pat. No. 4,147,545), an aqueous developer for negative-working or positive-working reproduction layers is known, which contains a lithium salt of an acidic organic compound and/or an amphoteric surfactant. In an extensive listing, lithium benzoate, lithium naphthenate and lithium acetylsalicylate are also mentioned, inter alia, as suitable lithium salts.
The process for developing positive-working or negative-working reproduction layers according to German Offenlegungsschrift No. 2,504,130 is carried out at temperatures from 35.degree. to 80.degree. C. with developers, the components of which have a boiling point (b.p..sub.760) higher than 80.degree. C. The developer can, inter alia, contain an organic solvent, a component having an alkaline reaction, an anionic or nonionic surfactant, water and/or an antifoaming agent, which, inter alia, is also to include benzoic acid in a proportion of 0.1 to 5% by weight.
German Offenlegungsschrift No. 2,934,897 (=WO-OS No. 79/00,593) describes a desensitization solution for negative-working reproduction layers, which contains (a) 2 to 50% by weight of a substituted benzoic acid, a substituted benzenesulfonic acid or benzenephosphonic acid or of a corresponding salt of these acids and (b) 5 to 60% by weight of a filmformer selected from the group comprising aliphatic polyols, monoesters or alkali metals salts thereof. As suitable components (a), sodium benzoate, 4-hydroxybenzoic acid or the potassium or sodium salt of 4-aminobenzoic acid are mentioned. The desensitization solution is said to also be suitable as a developer for the above-mentioned layers.
European Patent Application No. 0,033,232 discloses a developer for negative-working reproduction layers, which contains (a) 20 to 300 g/l of a salt of an aliphatic carboxylic acid having up to 9 C atoms, (b) a non-ionic surfactant and, if appropriate, (c) 20 to 300 g/l of a salt of an aromatic carboxylic acid. Salts of benzoic acid or toluenecarboxylic acid are mentioned as a suitable component (c).
Many of the known developers have, however, either the disadvantage of a relatively high pH value, as a result of which, for example, the aluminum oxide layers present on many printing plate support materials can be attacked, or they contain organic solvents, so that developing in a manner which does not pollute the environment is not ensured in the optimum manner. The hitherto disclosed salts of aliphatic or aromatic carboxylic acids can admittedly develop some reproduction layers, but problems arise, in particular in the case of layers containing binders. Although the addition of certain surfactants can assist the developing process, and this applies in particular to reproduction layers which are to be developed by hand or in troughs, foaming effects frequently occur when these developers are used in automatic developing machines.